Refractory linings for chambers for degasifying metals



United States Patent Office 3,203,785 Patented Aug. 31, 1965 9 Claims.in. 7s-49 Vacuum chambers with highly refractory linings made, forexample, of magnesite blocks, are frequently used for degasifying metalssuch as steel. It has been found that the durability of the chamberlinings is considerably inferior to that of similar linings of othermetallurgical apparatus. This is because slag introduced into thedegasifying chamber with the molten metal infiltrates into the liningwith the resultant deterioration of the lining. This deterioration isparticularly noticeable under reducing conditions. It is virtuallyimpossible when charging the chamber with molten metal to prevent someslag from entering the chamber.

In accordance with the present invention the durability of such liningsis increased by covering them with an aluminum oxide and silicon dioxidecoating which is viscous at operational temperatures. The coating, whichmay be approximately 2 to 3 mm. thick may also contain magnesium oxideand a fiuxing agent such as fiuorspar.

The coating may be applied to the lining in a number of different waysas exemplified in the following examples.

In a first example, a pulverulent mixture of aluminum oxide and silicondioxide, preferably containing a fiuxing agent and some magnesium oxide,is applied to the lining when cold. The vacuum chamber is subsequentlybrought up to its operational temperature in the usual way whereupon=the protective coating becomes viscous. In this state it covers themasonry lining uniformly and closes the surface pores of the lining.This prevents the infiltration into the refractory masonry of slag whichenters the vacuum chamber together with metals to be degasified.

In a second example, the refractory lining of the chamber is providedwith two protective layers, the bottom consisting of pure sand and thetop one, of a pulverulent mixture of aluminum oxide and silicon dioxide,again preferably with a fluxing agent and some magnesium oxide. Thechamber is subsequently heated to operational temperature and the twocoatings produce a viscous layer which protects the lining bypenetrating into and closing the pores of the lining blocks as before.

In a third example, an initial charge of molten steel or other metal tobe degasified in the vacuum chamber is drawn oft slag free from afurnace in a ladle and it is then covered with a synthetic slagconsisting of aluminum oxide and silicon dioxide, preferably againtogether with a fluxing agent and some magnesium oxide. The metal andthe synthetic slag are then introduced into the vacuum chamber and theslag remains in the form of a viscous coatings on the chamber liningafter the steel has been degasified and drawn off from the chamber. Asan alternative step, the artificial slag may be introduced into thechamber separately after the slag free metal has been introduced intothe chamber to 'be degasified.

The protective coating on the lining should be renewed afterapproximately every tenth charge.

A particularly suitable composition of the protective coating has beenfound to consist of 55% sillimanite A1 0 35% SiO 30% MgO; 10% A1 0 and5% fluorspar.

I claim:

1. A method of increasing the durability of refractory linings coveringthe interior of vacuum chambers for degassing molten steel, the stepsof, covering said lining with a pulverulent mixture of aluminum oxideand silicon dioxide which is viscous at the pouring temperature ofmolten steel, and heating said vessel to the pouring temperature ofmolten steel whereupon said coating becomes viscous.

2. A method of increasing the durability of refractory linings of Vacuumchambers for degassing molten steel, the steps of, covering slag freemetal to be degassed with a slag containing aluminum oxide .and silicondioxide, introducing the molten metal into said vacuum chamber fordegassing, and withdrawing the molten steel from said chamber to coatsaid lining with said slag.

3. A method of increasing the durability of refractory linings of vacuumchambers for degassing molten steel, the steps of, drawing slag freemolten steel into said chamber, introducing into said chamber a slagconsisting of aluminum oxide and silicon dioxide to cover said moltensteel, and withdrawing the molten steel from said chamber to coat saidlining with said slag.

4. A vacuum chamber for degassing molten steel, a refractory liningcovering the interior of said chamber, a coating covering said liningand including aluminum oxide and silicon dioxide, said coating beingviscous at the pouring temperature of molten steel.

5. The chamber set forth in claim 4 wherein said coating also includesmagnesium oxide.

6. The chamber set forth in claim 5 wherein the coating also includes afiuxing agent.

7. The chamber set forth in claim 6 wherein said fluxing agent isfluorspar.

8. The chamber set forth in claim 4 wherein the coating consists of 55%sillimanite (55 A1 0 35% SiO 30% magnesium oxide, 10% aluminum oxide and5% fiuorspa-r.

9. The chamber set forth in claim 4 wherein said lining has a base layerof sand and said coating is disposed on said sand.

References Cited by the Examiner UNITED STATES PATENTS 1,198,827 9/16Davies -95 1,663,660 3/28 Hottinger 266-43 1,789,474 1/31' Orwick 266-432,177,716 10/ 39 Heuer 266-43 2,631,344 3/53 Kennedy 75-50 DAVID L.RECK, Primary Examiner.

1. A METHOD OF INCREASING THE DURABILITY OF REFRACTORY LININGS COVERINGTHE INTERIOR OF VACUUM CHAMBERS FOR DEGASSING MOLTEN STEEL, THE STEPSOF, COVERING SAID LINING WITH A PULVERULENT MIXTURE OF ALUMINUM OXIDEAND SILICON DIOXIDE WHICH IS VISCOUS AT THE POURING TEMPERATURE OFMOLTEN STEEL, AND HEATING SAID VESSEL TO THE POURING TEMPERATURE OFMOLTEN STEEL WHEREUPON SAID COATING BECOMES VISCOUS.